Many of the item attributes in the response are used in future cart requests.
Those item attributes are explained in the following table.

Attribute

Description

CartId

An alphanumeric token that uniquely identifies a remote
shopping cart. This value must accompany every cart operation
associated with the newly created cart.

HMAC

Hash Message Authentication Code. This is an encrypted
alphanumeric token used to authenticate requests. A URL-encoded
version of this value must accompany every cart operation
associated with the newly created cart. The alternative is to
include, instead, the URLEncodedHMAC value.

URLEncodedHMAC

This is the
HMAC
value with all of the characters converted in to a
URL-compliant form. Some
HMAC
characters, such as plus (+), are incompatible with URLs.
This is a problem because the
HMAC
must be included in every cart operation and thus is part
of the URL request. The
URLEncodedHMAC
value, then, is a convenience function that relieves
developers of the need to create their own URL-encoded
HMAC
value. This value must accompany every cart operation.

This is the URL that is submitted, like a request, to
enter the Order Pipeline and purchase the items in a cart.
PurchaseURL
includes the Associate's Tag. It is important that
this URL is used to make the purchase otherwise the
Associate will not get credit for the sale.

An alphanumeric token that uniquely identifies an item in the
cart. Although the items added to a remote shopping cart using
CartCreate
were identified by an
ASIN
or
OfferListingId, those items lose those
associations. Instead, to refer to an item in a cart in future
cart operation requests, you must use the item's
CartItemId
value.